1. Field of the Invention
The present invention relates generally to a closed type compressor for use in cooling, refrigeration or air-conditioning and, more particularly to, a closed type compressor which has an improved structure for coupling a refrigerant inducing or discharging pipe means to a cylindrical casing of the compressor.
2. Description of the Prior Art
A closed type compressor is constructed such that a compressor unit and an electric motor are housed in a hermetic casing. The closed type compressor is equipped with pipe means respectively for inducing or discharging refrigerants or coolants to or from foreign devices, e.g., evaporaters. The casing of the compressor has generally a cylindrical side wall, and at least one of the inducing pipe and the discharging pipe is often needed to be coupled to the compressor unit through the cylindrical side wall of the casing.
Usually, the casing is made of steel, while the pipes are made of copper. A coupling of the copper pipe to the steel casing has been made with an aid of a pipe joint made of steel from matters of a welding and a mechanical strength between them. The pipe joint comprises a cylinder portion whose inside wall fits well the outside wall of the copper pipe and a tapered flare portion extending from one end of the cylinder portion. The pipe joint is attached to the cylindrical side wall by fitting its cylinder portion into a circular aperture defined in the cylindrical side wall of the casing from inside thereof and engaging the flare portion with an aperture wall, defining the circular aperture, of the side wall. The pipe joint is then gas-welded to the cylindrical side wall around the aperture wall by a resistance welding. The pipe is soldered to the inside wall of the cylinder portion of the pipe joint with soldering brass or soldering copper.
The conventional closed type compressor had a drawback that the welding of the pipe joint to the cylindrical side wall of the casing often left some unwelded gaps between them. This was due to the fact that the tapered flare portion of the pipe joint is unable to contact to all the circular aperture wall perpendicularly of the cylindrical side wall of the casing, due to the fact that the side wall of the casing is cylindrical while the flare portion of the pipe joint is conical. Therefore there are left some unwelded sections as gaps between the circular aperture wall and the flare portion of the pipe joint. The gaps left unwelded reduce the hermeticity of the casing so as to cause a leakage of the coolant. Furthermore, the unwelded portions reduced the mechanical strength of the coupling portion between the casing and the pipe joint.
The resistance welding or a ring projection welding is practiced by flowing an electric current to a resistive contact portion between members to be welded together. The current flowing in the resistive contact generates a large quantity of heat which melts the contact portion. The heat quantity Q in the resistance welding is given by the following equation: EQU Q=0.24.multidot.I.sup.2 .multidot.R.multidot.t
where I is the current, R is the resistance at the contact portion including internal resistances of both members to be welded together, and t is the time the current flows.
The above described resistance welding is practiced for the contact portion between the casing and the pipe joint by pressing electrodes of a resistance welding machine against the casing and the pipe.
The resistance welding has a feature that the welding is easily applied in an automated manufacturing process so that the manufacturing cost is reduced. However, the resistance welding has a drawback that the welding is limited in its application by the requirement of a matching state between the shapes of the members to be welded together. To comply with the drawback in the field of manufacturing a closed type compressor, some methods have been conventionally used for ensuring a sufficient contact between the pipe joint and the casing. In one method, for example, the cylindrical side wall has been reshaped to a flat condition at its portion around the aperture for receiving a pipe joint. In another method, the cylindrical side wall has been burred at its portion around the aperture wall so as to produce a portion shaped to match the conical flare of the pipe joint. However, the conventional methods have still borne a drawback that the process of flattening or burring is added in the manufacturing process to cause an increasing of costs for manufacturing the closed type compressor.
There has been a further conventional method for coupling a pipe to a cylindrical side wall of a compressor casing. In that method, the pipe is fit into an aperture for receiving the pipe without using a pipe joint, and then gas-welded directly to an aperture wall with soldering silver. However, this method has still had some drawbacks. The gas-welding with soldering silver is not only very expensive in comparison to the total of costs for the resistance welding and a pipe joint, but also the soldering silver is more expensive than the soldering copper or the soldering brass. The gas-welding of the pipe directly to the aperture wall with the soldering has of course a drawback that the gas-welding is difficult to apply in the automated manufacturing process as aforementioned.